You need to sand the beadboard and trim smooth. This won't be easy, the paint will gum up your sand paper. Start with 150 grit, if this doesn't cut it use 120 grit. Keep the sandpaper or palm sander moving across the flat surfaces. Use a sanding sponge for the trim and the hard to reach areas. Remove the dust with a vacuum with a brush attachment then wipe with a damp soft cloth.
Now apply 2 coats of Kilz Original Oil Base primer. Allow each coat to dry for one hour between each coat. Allow 24 hours (overnight) for the 2 coats of Kilz to dry. Now lightly sand with a 180 grit sanding sponge. Remove the dust with a vacuum then wipe with a damp soft cloth. This will produce a very smooth surface for painting.